Pulse width modulation system



Feb. 17, 1959 K G, HERNQWST l 2,874,355

PULSE WIDTH MCDULATION SYSTEM Filed Jan. 2., 1957 2 Sheets-Sheet 1 mm U f INVENTOR.,

' Afro/wir Feb. 17,

Filed Jan.

1959 K. G. HERNQvls-r 2,874,355

PULSE WIDTH MCDULATION SYSTEM 2, 1957 2 Sheets-Sheet 2 f4 I ffm/5- KWILILHJJLHL VEN TOR.

HTTJR/VEY i' 2,874,355 `PULSE WIVD'IH MODULATION SYSTEM AKarl G. Hernqvishlrincetom MN.' J.,` assigner to Radio 'Corporation oi?A America, a corporation of Delaware Application January 2, 1957, Serial No. 632,081

18 Claims. (CL 332-8) This 4invention relates-to a pulse system, and particularly lto a` novel method of and means for controlling the generation of `pulses usefull-in modulation and radar sys- -tems.

An object-of thefinvention-is to provide a pulse com- .munication system which makes use of the fast switchl ing `action of an ignitron type tube.

Another object of the-inventionis to provide a switching device which will handle a large amount of power :and also provide pulses of controllable-width at relatively high repetition rates for modulation purposes.

l Still another object of the invention is to provide an improvedmeans for the generation of pulses of sufficient power suitable for the modulationof a radar transmitter, nor` for usein telemetering applications.

.- Brieily stated, theinventioncomprises a pulse generating system including an. ignitron-,type tube employedto control the duration. ofthe pulses used for modulation purposes. In the operation ofthe system, the ignitron is started or fired at the beginning of a control pulse, and then cutoff or extinguished by applying a negative pulse .both tof themain anode and the holding anode of the ignitron typetube. The precise timeof occurrence of the vnegative pulse is controlled, by..an input modulating signal, thus enabling the i-gnitronto.generatepulses of con- This-.may be appreciated from, the Vfact that a mercury pool arc `such as used in an ignitron tube can be extinguished in a period of from l8 to 10*9 seconds.

The ignitron type tube used u in the modulation systemY -of the invention contains a starting proberan arc-holding anode, a main anode, acontrol grid shielding the main anode, Vand a mercury pool or liquid cathode. An arc is joined from the mercury pool cathode tol the holding anodey byrfeeding a positive pulse from a lgenerator to theV starting probe. The p'ulsegenerator also feeds a trigger pulse to iirst and second time delay circuits. The

,first time delay circuit feeds a trigger.` pulse to the. controlgrid of the ignitrontype tube after a predetermined period of time from the tiring of the turbe to draw the are from the holding anode t0 thel main anode. In one'einb odiment of Vtheginvention, thetsecond time delay circuit serveswto combine anV input modulating signal with the pulse fed ,-to it from the pulse generator in order to. send a modulated trigger pulse to thegrid of a Ythyratron tube. The thyratron tube provides a discharge `path for ay storage condenser through thefprimary winding of a` transformer. When `thestorage condenser is discharged, a .negativerpulse issrgenerated iin-two secondarywindings on the transformer. `One, secondary winding-feeds the `negative pulse through acoupling condenser tothe main anode of` the ignitronntube toextinguish the arcV to the 1main anode. At the same time. the other secondary wind- `ing of the transformer *feeds a negative pulse through a coupling condenser to the holding anode of the ignitron vtube to extinguish the arc` to-theV holding-anode. The holding anode is connected to -the positive terminali of a source of unidirectional potential through a first pulse forming network. Outputof the-ignitron `tube ine-the form of pulses is VVfed from the main-anode through a second pulse forming network to an output transformer. f The output transformer is connected .to the tube in a transmitter to be modulated, for example, a magnetron-oma klystron.

' Theleading edge ofthe-output pulse from-the system (derived from the mainanode of the ignitron) is defined by the application of the trigger pulse to the control-grid of theignitron tube While the trailing edge of the Ioutput pulse is defined by the application of a negative pulse to the anode o-'the ignitron tube which extinguishesrthe mercury arc. The period of pulse durationfis varied-in accordance with an input modulation signal fed tothe In another embodiment of thel invention, the width of the output pulse is varied manually by adjusting the/.tap on a voltage dividerin-the delaycircuit controlling ythe discharge of the storage condenser, rather than by applying an input modulating signal to the second time delay circuit.

-A more detailed description -of the inventionV follows in conjunction with thefdrawing, wherein:

Figure 1 is a schematic presentation of a pulse `width modulation system in accordance withone embodiment of the invention. Y

Figure 2 is a schematic vdiagram, of the time delaycircuit controlling thegrid of the thyratron tube, including means to provide a modulatedtrigger pulse.

Figure 3is a schematic diagram of the pulse forming network connected to the holdinganode of the ignitron type tube, which may be usedin the embodiment yofthe invention shown in Figure l.

Figure 4 is a schematic diagram of the output pulse forming network which "may be connected to themain anode of the ignitron Vtype tube in the embodimentof Figure 1.

Figure 5 is a chart of thewaveforms generated in the pulse. width modulation system illustrating vthe .time

vsequence inthe operation oftheV system.

Figure 6 is a graphillustrating the variation in output pulse width, of the modulation system for a sine wave input modulation signal.

Referringto Figure lin-detail, there is shown; an ignitron type tube. 1 having a Vcathode' composed .ofl a liquid or mercury pool 3 at ground potential, a starting probeS, a holding anode 7 a control grid 9-and a `main anode 11. The starting probe 5 is connected toapulse generator 11i .overilead 6. Pulse generator 13 feedsy a positive pulse to the Ystartingprobe` 5 to vaporize -the mercury pool 3 and startV anv arc between pool-'3 Vand holding anode 7. Pulse generator 13 also feeds a positive trigger-pulse to a tirst` time delay circuit 15 and-also to a second time delay circuit 17. The lirst time delay circuit 15 sends a positive trigger-pulse, over lead 14 to the control grid of the ignitron type tube 1 after a period of time T measured from the ring of the tube, -in order to draw thearc from the holding anode 7v to the main anode 11.` The first time delay circuit l5 is ofthe conventional type. Thefsecond time delay circuit 17V-.is composed of a multivibrator arrangement which will be .describedingreater detail ing connectionwith Figure ,2.

The output jot-the second time delay circuit 17 is vconnected to the grid VV19 of a thyratron gas tube" 21. The time'delay circuit 17 combinesV an input modulation rsignal from an input terminall 16-with the positive VYp ulsefrom fthek pulse V.generator .13 Ato .provide a" modulated `"trigger pulse for the thyratron tube 2'1. The cathode 23' of the `thyratron tube is at ground potential. The anode of the thyratron tube is connfected through a current limiting coil 27 to the positive terminal 26 of a unidirectional source of high positiveA potential. Anode 25 is also connected through a storage condenser 29 to the primary winding of a transformer 31. g

Transformer 31 has two secondary windings. One secondary winding is connected through a coupling condenser 33 to the anode 11 of the ignitron type tube 1 over lead 34. The other secondary winding 20 is connected through a coupling condenser 35 to the holding anode 7 over lead 36. A pulse forming network 37 is connected to the holding anode 7 at one end and to the positive terminal 38 of a source of unidirectional potenitial at the other end. A detailed description of pulse forming network 37 will be given in connection with `Figure 3.

After a period of time T2 from the tiring of the ignitron type tube the time delay circuit 17 sends a modulated trigger pulse to the grid 19 of thyratron tube 21. The thyratron tube' res, allowing storage condenser 29 to discharge through the primary winding of transformer 31. The discharge ofY storage condenser 29 forms a negative pulse in the two secondary windings 20 and 30 of transformer 31. One secondary winding 30 sends a negative pulse to the main anode 11 of the ignitron type tube 1 to extinguish the arc to the main anode. The other secondary winding 20 sends a negative pulse to the holding anode 7 to extinguish the arc to the holding anode.

The anode 11 of the ignitron type tube is connected through a pulse forming network 39 to B+ which is at the positive terminal 40 of a source of unidirectional potential. Pulse forming network 39 is connected to the primary winding of an output transformer 43. The secondary winding of the output transformer 43 is connected to the tube tov be modulated in the transmitter 44. The output pulse repetition rate may, for example, be of the order of 40 kc. The pulse forming network 39 will be described in greater detail in connection with Figure V4. y Figure 2 is a schematic diagram of the time delay circuit 17 showing a multivibrator arrangement composed of regeneratively intercoupled vacuum tubes 45 and 53. The cathode 47 of tube 45 is connected to ground through a resistor 61 which is common to cathode 55 of tube 53. Grid 49 of tube 45 is connected to a movable tap on voltage divider 63. Voltage divider 63 is connected between positive terminal B+ and ground. A resistor 65 is connected from B+ to the input trigger pulse terminal 67. The positive input trigger pulse supplied to terminal 67 from the pulse generator 13 is fed through a coupling condenser 69 and a crystal rectifier 71 to the junction of anode 51 of tube. 45 and resistor 73. 4The other end of resistor 73 is connected to B+. Anode 51 is also connected through a coupling condenser 75 to the grid 57 of tube 53. A voltage divider 77 is also connected to grid 57 at one end and to the positive terminal B+ at the other end. The center tap of the voltage divider 77 is connected through a coupling condenser 79 to the input modulating signal terminal 16. Anode 59 of tube 53 is connected to B+ through a resistor 83. The ou"- put of tube 53 is fed .from the anode 59 through a coupling condenser to grid 87 of an amplifier vacuum tube 89. Grid 87 is connected through resistor 91 and a bias' battery 93 to ground. Cathode 95 is connected through resistor 97 to ground. The anode 99 of tube 89 -is connected to B+ through resistor 101. The output trigger pulse is fed through coupling condenser 103 to terminal 105 which connects with the grid 19 of thyratron 21 over lead 18. The pulse generator 13 supplies a trigger pulse having a constant repetition rate to the free running multivibrator. When an input modulation 'signal' is fed to themultivibrator via terminal 16 and the voltage divider 77, themodulation signal either adds or rsubtracts from the amplitude of the trigger pulse applied 'shown in Figure 1.

Y tube.

via terminal 67, resulting in a corresponding variation in pulse output width of the multivibrator. The variation in pulse output width varies the instant or starting of conduction of the thyratron tube 21 by virtue of a differentiation action on the leading and trailing edges ofthe output pulses from the multivibrator and hence varies the width of the pulse output of the ignitron type tube 1.

Figure 3 is a schematic diagram of the pulse forming network 37 connected to the holding anode 7 of ignitron type tube 1. The pulse forming network includes four serially connected circuit limiting inductance coils 107, 109, 111 and 112. Coil 107 is connected to the holding anode 7 of the ignitron type tube 1. Coil 112 is connected to a source of relatively low positive potential at terminal 38 with respect to the positive potential available at terminal 40. A first condenser 113 is connected from the junction of coils 107 and 109 to a resistor 119. The other end of resistor 119 isconnected to ground. A second condenser is connected from the junction of coils 109 and 111 to the junction of condenser 113 and resistor 119. A third condenser 117 is connected from the junction of coil 111 and coil 112 to the junction of condenser 113 and the resistor 119. Condensers 113, 115 and 117 and resistor 119 form a delay network which dissipates the negative pulse fed to the holding anode 7. -The current limiting coils of pulse forming network 37 limit the current surge which takes place when holding anode 7 strikes an arc.

Figure 4 is a schematic diagram of the output pulse forming network 39 connected to the main anode 11 of ,the ignitron type tube 1. The pulse forming network 39 supplies B+ voltage to the main anode 11 of the ignitron type tube 1 and prevents acurre'nt surge when an arc is struck to the main anode 11. The pulse forming network is composed of four serially connected current limiting inductance coils 123, 125, 127 and 129. Coil 123 is connected to the main anode 11 of the ignitron type tube 1. Coil 129 is connected to a source of high positive potential B+ at terminal 40. A first condenser 131 is connected from the junction of coils 123 and 125 to the primary winding of transformer 43. A second condenser 133 is connected from the junction of coils 125 and 127 to the junction of condenser 131 and the primary winding of transformer 43. A third condenser 135 is connected from the junction of coils 127 and 129 tothe junction of condenser 133 and the primary Winding of .transformer 43. The Condensers 131, 133 and 135 pro- Yvide a delay network for the output pulse of the system.

The amount of delay provided by pulse forming network 39 must be greater than the pulse duration of the output pulse of the ignitron type tube 1. l

FigureS is a chart of the waveforms generated in the pulse width -modulation system showing the time sequence in the operation of the system. Waveform A represents the starting voltage pulse applied to the starting probe 5 'of the ignitron type tube 1 by pulse generator 13 as Waveform B represents the current flowing through the holding anode of the ignitron type the holding anode 7 will pick up the arc at approximately the time TL after the application of the starting voltage. The time constant Th of the pulse forming network 37 must be larger than the maximum expected starting time lag TL max. Waveform C represents the trigger pulse from pulse generator 13 which is fed through the time delay circuit 15 to the control grid 9 of the ignitron type tube 1 and which causes the arc to transfer from the holding anode 7 to the main anode 11. The time delay T1 yof. time delay circuit 15 must be larger than TL max but less than Th to insure that a holding arc is burning at the time the trigger pulse is applied to the control grid 9 to draw the arc to the main anode 11 of the ignitron type tube 1. Under these conditions it is possible to reduce the starting time ofthe arel to the main anode 11 Depending on the time lag TL in starting an arc,l

to below millimicro seconds. Waveform D represents the main anode current of the ignitronttype tube 1. The time constant of pulse yforming network 39`must be larger than the largest pulse output widthv of the ignitron type tube 1. Waveform E represents the positive .trigger voltage pulse fed by the pulse generator 13 through the time delay circuit 17 to the grid 19 of the thyratron tube 21.. The time delay T2 of time delay circuit 17' is' varied with the modulation signal and determines the time of cessation or the pulse width of the main anode current represented by the waveform D.

Figure 6 is a graph illustrating the variation in pulse output width of the modulation system for a sine wave input modulating signal. Waveform A represents a seriesV of 'output pulses from the transmitter 44 when. they are not modulated by a message or intelligence applied to terminal 16 of Figure l. Waveform B represents the sine wave input modulating signal 'applied to the time delay `circuit 17' of the pulse width modulation system. Waveform C represents' the variation in output pulse width when the pulse width modulation system is used to modulate the transmitter output pulses represented by the waveform A. Y

The invention may be used in any application where it is required to vary the pulse duration as in communications, interrogation radar and telemetering systems. As indicated in Figure 4, the secondary winding of transformer 43 may be connected to the input circuit of a magnetron or a klystron in the transmitter 44, the transmitter 44 being included in a itelemetering or other pulse system.

The term ground used herein is not limited to an actual earth connection but is deemed totinclude any point of reference potential.

What is claimed isz'.

1. A pulse width modulationsystem comprising in coinbination an ignitron type tube having a-mercury pool cathode, a starting probe, a holding anode, acontrol grid and a main anode, means for applying a positive potential to `said holding anode, means for applying a positive potential to said main anode, a pulse generator, said pulse generator being coupled to said starting probe toV supply` a pulse of positive potential thereto for vaporizing said mercury pool to cause an arc from said pool to said holdinganode, a first delay circuit coupled between said pulse generator and said control grid, saidpulse generator being adapted to feed a trigger pulse through said tir-st delay circuit to ysaid control gridof-su-icient magnitude to draw an arc to said main anode, means including a second delay circuit to apply a negative pulse (to said` main anode and said holding anode for extinguishing the arc to said main anode and said holdingA anode, means for applying an input modulating signal to 'said second delay circuit for varying the time of occurrence of said negative pulse, and means for deriving an output pulse from said ignitron, the output pulse varying in width in accordancek with said input modulating signal.

2.' A pulse width modulation system bination an ignitron type tube having a mercury pool cathode, a starting probe, a holding anode, a control grid and a main anode, a first current limiting means for applying a positive potential to said holding anode, a second current limiting means for applying a positive` potential to said main anode, a pulse generator, said pulse generator `being coupled to said-starting probe to supply a pulse of positive potentialthereto for vaporizing said mercury pool to cause an arc from said pool to lsaid holding anode, a first delay circuit coupled-'between said pulse generator and said control grid, said pulse generator being adapted to feed a trigger Vpulse through said first' delay circuit to said control grid` of sucient rnagnitude to draw an arc to saidY main anode, means including a second delay circuit to apply a negative pulse 'to said main anode and said holding anode for extinguishing the arc to said'znain 1anode and'said holding anode, means comprising in com-v atl for applying an input modulating signal to said second delay circuit for varying the time of occurrence of said negative pulse, and means for deriving an output pulse from said ignitron, the output pulse varying in widtlr in accordance with said inputmodulating signal.

3. A pulse width modulation system as claimed in claim 2, wherein said irst and second current limiting means comprise rst and second pulse forming networks, said first pulse forming network being connected to the positive terminal of a unidirectional source of low potential; said 'second pulse forming network being connected to the positive terminal of a unidirectional source of high potential.

4'. A pulse width modulation system comprising in combination an ignitron type tube having a mercury pool cathode, a starting probe, a holding anode, a control grid and a main anode, a first pulse'forming network, said irst pulse forming network Ibeing connected atV one erid` to the positive terminal of a vunidirectional source of low potentiall and at the other end to said holdingv anode, al second pulse forming network, Said second pulse forming' network being connected atone end to the positive terminal of a unidirectional source of high potential andi at the other end to said main anode, a pulse generator supp-lying a pulse of positive potential to 'saidy starting probe for vaporizing said mercury pool to cause an are' from said pool to said holding anode, a rst delay circuit coupled between said pulse Vgenerator and saidV controlgrid, said pulse generator being adapted to feed a trigger pulse through said rst delaycircuit to said control grid of su'icient magnitude to draw an arc lto said main anode, meansV to apply a negative pulse to saidmain anode and said holding anode for extinguishing the arc'to said main anode and said holding anode, a second delay cir'cuitf,` said second delay circuit being coupled between said' pulse generato-r and said means, saidV pulse generator being adapted to feed a trigger pulse to 'said seco-nd delay circuit` for controlling said means, means for applying an input modulating signal tol said second delay circuit for varying the time of `said negative pulse applied by said irste mentioned means, and means for deriving an output pulse from said ignitron, the output pulse varying in width in' accordance with said input modulating signal.

5. A pulse width modulation ysystem comprisingV in combination an ignitron type tube having a mercury pool cathode, a starting probe, a holding anode, a control grid and a main anode, a `rst'pul'sel forming network, said first pulse forming network being connectedv at one end to the positive terminal of a'unidirecti'onal source of low potential and Vat the other end to said holding anode, a second pulse forming network, said second pulse forming network being connected at one end-to the positive terminal of a unidirectional source of' high potential and at theother end to said main anode, a

pulse generator, said pulse generator supplying a pulse of positive potential to said starting probe for vaporizing said mercury pool to cause an arc from said poolto said holding anode, a first delay circuit coupled between' said pulse generator and saidcontrol'grid, said pulse generator being adapted to feed a iirst trigger pulse through said iirst delay circuit to said control grid of sufficient magnitude to draw an arc to -said main anode, a thyratron tube connected serially with storage means, said storage means being adaptedrupon the triggeringV of said thyratron tube to apply negative pulses to said main anode and saidrholding anode for extinguishing the arc to said main anode and said holding anode, a second delay circuit, -said second delay circuit being coupled between said pulse generator and the grid of said thyr-atron tube, said pulse generator being adapted to feed a sec-VV ond trigger pulse to said second delay circuit for trig-V gering said thyratron tube, means for applying an-nputi modulatingfsignal to said second delay circuit for vary-- ing the time of the third trigger pulse fed to the grid-off said` thyratron tube, and means for deriving an output 7 pulse.V from said ignitron, the output pulse varying in width in accordance withV said input modulating signal.

6, A pulsetwidth modulationsystem as claimed in claim 5, said second delay circuit comprising a multivibrator, an amplifier stage, a coupling condenser and a rectifier, said multivibrator being coupled to said amplier, said coupling condenser being serially connected to said rectifier, said pulse generator being adapted to feed said second trigger pulse through said coupling condenser and said rectifier to said multivibrator, said input modulation signal being applied to said multivibrator, said multivibrator combining said second trigger pulse with said input modulation signal to form said third modulated trigger pulse for triggering said thyratron tube.

7. A pulse width modulation system as claimed in claim 5, said storage means comprising a storage'condenser connected in series with the primary winding of a transformer and said thyratron tube, said transformer having two secondary windings, one of said secondary windings being connected through a coupling condenser to said main anode, the other of said secondary windings being connected through a coupling condenser to said holding anode, the discharge of said storage condenser upon the triggering of said thyratron tube forming a negative pulse in said secondary windings, said negative pulse extinguishing the arc to said main anode and said holding anode.

8. A pulse width modulation system as claimed in claim and wherein said 'means for deriving said output pulse includes an output transformer having a primary and a secondary winding, said primary winding being connected through said second pulse forming network to said main anode and said secondary winding being connected to a load.

9. A pulse ywidth modulation system as claimed in claim 5 and wherein said means for deriving said output pulse includes an output transformer having a primary and a secondary winding, said primary winding beingr connected through said second pulse forming network to said main anode and said secondary winding being connected to a klystron.

10. A pulse width modulation-system as claimed in claim 5 and wherein said means for deriving said output pulse includes an output transformer having a primary and a secondary winding, said primary winding being connected through said second pulse forming network to said main anode, said secondary-winding bengconnected to a magnetron.

, l1. A pulse width modulation system as claimed in claim 5 and wherein said means for deriving said output pulse includes Van output transformer having a primary anda secondary winding, said primary winding being connected through said second pulse forming network to said main anode, said secondary winding being connected to a telemetering system. Y

.v 12. VA pulse width modulation system comprising in combination an ignitron type tube having a mercury pool cathode, a starting probe, a holding anode, a control grid and a main anode, a lirst pulse forming network, said first pulse forming network being connected at one end to the positive terminal of a unidirectional source of low potential and at the other end to said holding anode, a second pulse forming network, said second pulse forming network being connected at one end to the positive terminal of a unidirectional source of high potential and at the other end -tosaid main anode, a pulse generator, said pulse generator supplying apulse of positive potential to said starting probe for vaporizing said mercury pool to cause an arc from said cathode to said'holding anode, a first delay circuit coupled betweensaid pulse generator and said control grid, said pulse generator being adapted to feed a rst trigger pulse through said iirst delay circuit to said control grid of sufficient magnitude to draw an arc to said mainanode, a thyratron tube, a

storage condenserand a transformer having a primary and two secondary windings, said thyratron tube being serially connected to said storage condenser and the primary winding of said transformer, first and second coupling condensers.oneof said secondary windings being connected through 4said lirst coupling condenser to said main anode, the other of said secondary windings being connected through said second coupling condenser to said holding anode, a second delay circuit, said pulse generator being adapted to send a second trigger pulse through said second delay circuit for triggering said thyratron tube to cause said storage condenser to discharge through said primary vwinding and said thyratron tube, the discharge of said storage condenser forming negative pulses in saidsecondary windings, said negative pulses extinguishing the are to said main anode and said holding anode, and an output transformer having a primary and a secondary winding, the primary winding of said output transformer being connected through said second pulse forming network to said main anode for deriving an output pulse from said ignitron for application from the secondary winding of said output transformer to a utilization circuit.

13. A pulse width modulation system as claimed in claim l2 and wherein said second delay circuit is responsive to a modulating input-signal applied thereto to vary the time of said second trigger pulse according to the amplitude of said signal, said ignitron being operated according to the triggering time of said thyratron in response to said second trigger pulse to cause said output pulse to be of a width determined according to said amplitude of said signal.

14. A pulse width modulation system comprising, in combination, an ignitron type tube having a liquid cathode, a starting probe, a holding probe, a control grid and a main anode, a irstkpulse forming network connected at one end to a positive terminal of a unidirectional source of low potential and at the other end to said holding anode, a second pulse forming network connected at one end to a positive terminal of a unidirectional source of high potential and at the other end to said main anode, a pulse generator arranged to supply a positive pulse to said starting probe to cause an arc between said cathode and said holding anode, a first delay circuit, said generator being arranged to supply a first trigger pulse through said rst delay circuit to said control grid of suicient magnitude to cause an arc between said cathode and said main anode, said first delay circuit being arranged to control the time of said lirst trigger pulse so that said first trigger pulse is applied to said control grid after the arc is made between said cathode and said holding anode, a storage means, a second delay circuit to which a modulating input signal is applied, said generator being arranged to apply a second trigger pulse through said second delay circuit tosaid storage means, said second delay circuit being arranged to vary the timek of said second trigger pulse according to a given parameter of said signal, said storage means being responsive to said second trigger pulse to apply negative pulses to said main anode and said holding anode to extinguish the arc to said main anode and said holding anode, and means connected to said ignitron through said second pulse forming network for deriving an output pulse from said ignitron of a width determined according to said parameter of said signal.

15. A pulse modulation system comprising, in combination, an ignitron type tube having a liquid cathode, a starting probea holding anode, a control grid and a main anode, means for applying a positive potential to said holding anode and to said main anode, means for applying a pulse of the proper polarity to said starting probe lfor starting an arc between said cathode and said holding anode, means for subsequentially feeding a trigger pulse to said control grid of 'suicient magnitude to draw an are from said 'cathode to said main anode, an,

input circuit to which a modulating input signal is ap plied, means connected to said input circuit and responsive to said signal to apply a negative pulse modulated according to a given parameter of said signal to both said main anode and said holding anode for extinguishing the arc to said main anode and to said holding anode, and means connected to said tube for deriving from said tube an output pulse modulated according to said parameter of said signal.

16. A pulse width modulation system comprising, in combination, an ignitron type tube having a liquid cathode, a starting probe, a holding anode, a control grid and a main anode, means for applying a positive potential to said holding anode and to said main anode, means for supplying a pulse of proper polarity to said starting probe to cause an arc between said cathode and said holding anode, means for subsequently applying a pulse of the proper polarity and magnitude to said control grid todraw an arc from said cathode to said main anode, an input circuit to which a modulating input signal is applied, means connected to said input circuit and responsive to said signal to apply a pulse of the proper polarity time modulated according to the amplitude of said signal to both said main anode and said holding anode for extinguishing the arc to said main anode and to said holding anode, and means connected to said tube for deriving from said tube an output pulse of a Width determined according to said amplitude of said signal.

17. A pulse modulation system comprising, in combination, an ignition type tube having a mercury pool cathode, a starting probe, a holding anode, a control grid and a main anode, means for applying a positive potential to said holding anode and to said main anode,

iirst pulse to apply a second pulse to said control grid after the arc is made between'said cathode and said holding anode to draw an arc from said cathode to said main anode, an input circuit to which a modulating input signal is applied, a second means connected to said input circuit and responsive to said signal to apply a negative pulse modulated according to a given parameter of said signal to both said main anode and said holding anode for extinguishing the arc to said main anode and to said holding anode, and a third means connected to said tube for deriving from said tube an output pulse modulated according to said parameter of said signal.

18. A pulse modulation system as claimed in claim 17 and wherein said pulse generator operates simultaneously upon the application thereby of said rst pulse to said starting probe to apply a third pulse to said second-mentioned means, said second-mentioned means being operated upon the reception of said third pulse thereby to apply said negative pulse to said main anode and said holding anode.

References Cited in the tile of this patent UNITED STATES PATENTS' 2,269,842 Brown Jan. 13, 1942 2,534,261 Gorham et al. Dec. 19, 1950 2,654,856 Toulon Oct. 6, 1953 FOREIGN PATENTS 514,342 Canada July 5, 1955 

